I won an Asateri horse...tier 6...in a tournament. The trade-in value is 15K, so I suspect it is really rare. So, i am not selling it.

But, I am starting a new game so I am not high enough tier to ride it. WHERE DO I FIND MY TIER LEVEL SO I KNOW HOW CLOSE I AM TO BEING ABLE TO RIDE IT?

If you are playing Alpha Centauri, this is not an Asateri horse but a Battle Ogre Mk2. Be careful with these units as they can not be healed the regular way, the damage they take is permanent.

...beneath your eyes.

Chopping onions...

It depends on your riding skill, not the horse tier...
There's a specific forum for Mount & Blade games, btw ;)

But what does the wizard want?

I assume this is about Black Desert Online?

According to what little I was able to find, you can ride any horse in the game (at least, once you tamed it)?

So, maybe you need to "tame" your newly won horse first?

To do that, you need to "train" your taming skill to 5 first, by riding the donkey that you get at the beginning of the game, then you'll need lassos and sugarcubes.

Simply following along this guide, should help you, I guess:

https://gamerant.com/black-desert-get-horse-guide/

May I suggest reading the fine manual. They usually explain the user interface at least.